U.S. patent application number 12/933778 was filed with the patent office on 2011-01-27 for floating support fitted with a turret including rolling bearings out of the water.
This patent application is currently assigned to Saipem S.A.. Invention is credited to Michel Baylot, Jean-Paul Denise, Thomas Marty.
Application Number | 20110017117 12/933778 |
Document ID | / |
Family ID | 39967627 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110017117 |
Kind Code |
A1 |
Baylot; Michel ; et
al. |
January 27, 2011 |
Floating Support Fitted with a Turret Including Rolling Bearings
out of the Water
Abstract
An oil production floating support including a disconnectable
mooring system for anchor lines to the sea bottom and for
bottom-to-surface connection pipes. The floating support comprises
a mooring buoy for mooring lines and bottom-to-surface connection
pipes, the buoy preferably being an annular buoy. The floating
support being characterized in that said turret has a watertight
tubular outer structure having a bottom wall assembled in
watertight manner to the bottom end of the watertight tubular outer
structure. The tubular outer structure contains an inner structure
secured at its top end to the hull. The inner and outer tubular
structures co-operate with at least one bottom rolling or friction
bearing, enabling the inner structure to turn, with the outer
structure not being caused to turn when the floating support is
caused to turn about a vertical axis ZZ' of the cavity and of the
watertight tubular outer structure. The bottom rolling or friction
bearing being situated beneath the surface of the water, but inside
said watertight outer structure.
Inventors: |
Baylot; Michel; (Marseille,
FR) ; Denise; Jean-Paul; (Hyeres, FR) ; Marty;
Thomas; (Aix en Provence, FR) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE LLP
551 FIFTH AVENUE, SUITE 1210
NEW YORK
NY
10176
US
|
Assignee: |
Saipem S.A.
Montigny Le Bretonneux
FR
|
Family ID: |
39967627 |
Appl. No.: |
12/933778 |
Filed: |
March 18, 2009 |
PCT Filed: |
March 18, 2009 |
PCT NO: |
PCT/FR2009/050453 |
371 Date: |
September 21, 2010 |
Current U.S.
Class: |
114/230.12 |
Current CPC
Class: |
B63B 22/023 20130101;
B63B 22/026 20130101; B63B 22/025 20130101; B63B 21/508
20130101 |
Class at
Publication: |
114/230.12 |
International
Class: |
B63B 22/02 20060101
B63B022/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2008 |
FR |
0851832 |
Claims
1. An oil production floating support including a disconnectable
mooring system for anchor lines anchored to the sea bottom and for
bottom-to-surface connection pipes, the floating support
comprising: a mooring buoy for said anchor lines and first
bottom-to-surface connection pipes extending from said buoy, to
which they are moored, down to the bottom of the sea, said buoy
preferably being an annular buoy; a turret extending in a through
cavity passing along the entire height of the hull of the floating
support, said mooring buoy being fastened under the hull of the
floating support to said turret, said turret co-operating with the
hull within said through cavity passing along the entire height of
the hull of the floating support, said turret being rotatably
mounted relative to said hull via at least one rolling or friction
bearing, and preferably via a rolling bearing, so as to allow said
floating support to turn about a substantially vertical axis ZZ' of
said turret and of said cavity without causing said mooring buoy to
turn relative to the same vertical axis ZZ'; and second connection
pipes between the top ends of said first bottom-to-surface
connection pipes and the deck of the floating support, the second
pipes rising within the cavity to a coupling for a plurality of
said second pipes, said coupling being secured to the floating
support, preferably level with the deck of the floating support,
said coupling being of the rotary joint coupling type and being
rotatably mounted so as to allow said floating support to turn
without turning said coupling; the floating support further
comprising: a watertight tubular outer structure about the same
vertical axis ZZ', preferably of circular section, having a bottom
wall assembled in watertight manner to the bottom end of said
watertight tubular outer structure; said tubular outer structure
containing an inner structure, preferably a tubular inner structure
of circular section coaxial with said tubular outer structure, the
top end of said inner structure being secured to the hull; said
bottom wall of the watertight outer structure having a plurality of
said pipes passing therethrough in leaktight manner, which pipes
pass through and are supported by said inner structure; said
watertight outer structure not being supported by said hull nor
being fastened to said hull, and having dimensions that enable it
to float naturally in the water in the cavity in said floating
support; said inner and outer tubular structures co-operating with
at least one bottom rolling or friction bearing, preferably a
rolling bearing, allowing said inner structure to turn, said outer
structure being prevented from turning when said floating support
is caused to turn about said vertical axis ZZ' of the cavity and of
said watertight tubular outer structure; and said bottom rolling or
friction bearing being situated below the surface of the water but
inside said watertight outer structure.
2. The floating support according to claim 1, wherein at least one
"support" bottom rolling bearing interposed between the bottom wall
of said watertight tubular outer structure and the bottom end of
said inner structure.
3. The floating support according to claim 1, wherein: at least one
bottom "guide" lateral rolling bearing interposed between the inner
side surface of said outer tubular structure and the outer side
surface of said inner structure, said bottom lateral guide bearing
being situated below the level of the water surface and closer to
said bottom wall of said tubular outer structure than to the top
end of said tubular outer structure; and at least one top "guide"
lateral rolling bearing interposed between the inner side surface
of the outer tubular structure and the outer surface of said inner
structure, said bearing being situated closer to the top end of
said tubular outer structure than to the bottom of said tubular
outer structure.
4. The floating support according to claim 1, wherein said rolling
bearing(s) is/are constituted by rollers or by wheels.
5. The floating support according to claim 4, wherein said rollers
or wheels are disposed circularly around said inner structure,
preferably being regularly spaced apart in the annular space
between said inner and outer structures.
6. The floating support according to claim 1, wherein said outer
and inner tubular structures include abutment means and retaining
means preventing said outer structure from sinking in the event of
sea water accidentally flooding the inside of the outer tubular
structure by loss of watertightness, said abutment means and
retaining means enabling the outer structure to be retained by said
inner structure.
7. The floating support according to claim 1, wherein inner
structure includes at its top end a top peripheral plate via which
said inner structure is secured to the hull of said floating
support.
8. The floating support according to claim 7, wherein said top
plate bears against a step in the top end of said cavity,
preferably in such a manner that said top plate does not project
above the level of the deck of the floating support.
9. The floating support according to claim 1, wherein said inner
structure contains a carrier structure, preferably in the form of a
central pillar, preferably of circular section, that rests on the
bottom wall of said tubular outer structure and that extends up to
the level of the deck of the floating support, said carrier
structure holding said second pipes passing through the inner
structure in a supported position, and preferably also supporting
said rotary joint coupling resting on top of said carrier structure
level with the deck of the floating support.
10. The floating support according to claim 1, wherein said buoy
includes a top tubular wall, preferably of circular section,
defining a "valve" chamber when the top edge of the tubular top
wall of the buoy is pressed against the bottom wall of the turret,
said valve chamber containing the top ends of said first pipes
passing through the bottom wall of said valve chamber, the top ends
of said first pipes being fitted with vales and/or with male or
female automatic connector portions supported by said bottom wall
of the valve chamber, and said buoy including in its bottom portion
an annular box constituting a float under the bottom wall of the
valve chamber.
Description
[0001] The present invention relates to a floating support anchored
to a disconnectable turret.
[0002] The technical field of the invention is more particularly
the field of off-shore oil production in regions presenting extreme
ocean and weather conditions, and in particular in Arctic or
Antarctic regions, and working from floating supports.
[0003] In general, an oil production floating support has anchor
means to enable it to remain in position in spite of the effects of
currents, winds, and swell. It also generally includes drilling
means, oil storage means, and oil processing means, together with
means for off-loading to off-loading tankers, which tankers call at
regular intervals to take away the production. Such floating
supports or ships are conventionally referred to as floating
production storage off-loading (FPSO) vessels or indeed as floating
drilling & production units (FDPU) when the floating support is
also used for performing drilling operations with wells that are
deflected in the depth of the water. The abbreviation FPSO is used
below.
[0004] When weather and sea conditions, i.e. swell, wind, and
current are severe or even extreme, as during storms, it is
preferred to anchor the FPSO via a turret, generally situated in
known manner in the front half of the ship and on its axis, with
the ship being free to turn about said turret under the effect of
the wind, current, and swell. Thus, with wind, current, and swell
exerting specific forces on the hull and the superstructures, the
FPSO makes use of its freedom to turn about the vertical axis ZZ so
as to put itself naturally in a position of least resistance. The
pipes connecting it with the well heads are generally connected to
the underside of the turret and they are connected to the FPSO via
a rotary joint lying on the axis of said turret. When weather
conditions might become extreme, as in the North Sea, in the Gulf
of Mexico, or in the Arctic or the Antarctic, the FPSO is generally
disconnectable so as to be capable of taking shelter and waiting
for acceptable operating conditions to return.
[0005] The present invention relates more particularly to a
floating support for off-shore oil production in the Arctic or the
Antarctic, the support being fitted under its hull with a
disconnectable turret from where there extend anchor lines
connected to the sea bottom and bottom-to-surface connection pipes,
said hull including in its longitudinal direction substantially
plane sides that extend vertically, and possibly also in
conventional manner bow and stern portions (at the front and rear
ends of the ship) that are inclined relative to the horizontal and
that are preferably shaped so as to form a reinforced pointed stem
capable of breaking pack ice merely by bending it whenever said
pack ice forces it way under said reinforced stem.
[0006] Floating supports advantageously present a hull with
substantially vertical longitudinal sides in order to optimize
their oil storage capacities, and also to obtain better behavior in
heavy sea. However a hull with vertical sides is particularly
disadvantageous in terms of behavior relative to pack ice. Thus, in
U.S. Pat. No. 4,102,288 and U.S. Pat. No. 4,571,125, floating
supports are proposed that present, amongst other means, sides with
profiles that are curved or inclined so as to enhance ice breaking
in the manner that is known for a ship's bow having a stem that
slopes relative to the horizontal.
[0007] In known manner, an oil production floating support
including a releasable mooring system of anchor lines anchored to
the sea bottom and of bottom-to-surface connection pipes comprises:
[0008] a mooring buoy for said lines and bottom-to-surface
connection pipes, said buoy preferably being an annular buoy; and
[0009] said mooring buoy being fastened under the hull of the
floating support to a rotary device having a tower-shaped structure
referred to as a "turret", said turret being fastened to the hull
within a cavity passing through the entire height of the hull of
the floating support, said turret being rotatably mounted relative
to said hull via at least one rolling or friction bearing,
preferably a rolling bearing, so as to allow said floating support
to turn about a substantially vertical axis ZZ' of said turret and
of said cavity without causing said mooring buoy to turn relative
to the same vertical axis ZZ'; and [0010] said bottom-to-surface
connection pipes rise within the cavity to a coupling for a
plurality of said pipes, said coupling being secured to the
floating support level with the deck of the floating support, said
coupling being ratably mounted so as to allow said floating support
to turn without turning said coupling that is referred to as a
rotary joint coupling.
[0011] In the above-described prior art, the rolling bearing is
located either level with the deck of the floating support, or else
in the bottom portion under water, i.e. the bearing is immersed, or
indeed a combination of the above two configurations may be
used.
[0012] Embodiments in which the rolling bearing is located solely
level with the deck are suitable only for floating supports of
relatively small height, in particular less than 15 meters (m).
With greater heights, for floating supports having a height lying
in the range 20 m to 25 m, in particular, the horizontal force on
the turret resulting from the floating support turning gives rise
to the structure of the turret bending along its length, thereby
mechanically stressing the top rolling bearing and thus
mechanically endangering its reliability of operation. Furthermore,
when the rolling bearing is underwater in the bottom portion of the
turret, this immersion affects the operating reliability and the
durability of said rolling bearing, and above all gives rise to
difficulties in performing maintenance operations. On-site action
requires the use of divers and of considerable technical means, and
it is generally necessary to perform such operations in a protected
zone, such as a fjord, or better still in a dry dock, after the
FPSO has been disconnected. Thus, when an FPSO is intended to
remain in position for several tens of years without any programmed
maintenance disconnections in dry dock or in a protected site, that
type of turret is not suitable.
[0013] Supports of the above-defined type are known from GB 2 291
389, EP 0 259 072, and U.S. Pat. No. 4,604,961.
[0014] The object of the present invention is to provide a novel
floating support of the above-defined type with a disconnectable
mooring system that includes an improved rotary turret, and more
particularly one in which reliability and maintenance of the
rolling bearings used for enabling the turret to turn relative to
the floating support is improved, in particular by being simpler
and less expensive to perform and to implement.
[0015] To do this, the present invention provides an oil production
floating support including a disconnectable mooring system for
anchor lines anchored to the sea bottom and for bottom-to-surface
connection pipes, the floating support comprising: [0016] a mooring
buoy for said anchor lines and first bottom-to-surface connection
pipes extending from said buoy, to which they are moored, down to
the bottom of the sea, said buoy preferably being an annular buoy;
and [0017] a turret extending in a through cavity passing along the
entire height of the hull of the floating support, said mooring
buoy being fastened under the hull of the floating support to said
turret, said turret co-operating with the hull within said through
cavity passing along the entire height of the hull of the floating
support, said turret being rotatably mounted relative to said hull
via at least one rolling or friction bearing, and preferably via a
rolling bearing, so as to allow said floating support to turn about
a substantially vertical axis ZZ' of said turret and of said cavity
without causing said mooring buoy to turn relative to the same
vertical axis ZZ'; and [0018] second connection pipes between the
top ends of said first bottom-to-surface connection pipes and the
deck of the floating support, the second pipes rising within the
cavity to a coupling for a plurality of said second pipes, said
coupling being secured to the floating support, preferably level
with the deck of the floating support, said coupling being of the
rotary joint coupling type and being rotatably mounted so as to
allow said floating support to turn without turning said
coupling.
[0019] According to the present invention, said turret comprises:
[0020] a watertight tubular outer structure about the same vertical
axis ZZ', preferably of circular section, having a bottom wall
assembled in watertight manner to the bottom end of said watertight
tubular outer structure; [0021] said tubular outer structure
containing an inner structure, preferably a tubular inner structure
of circular section coaxial with said tubular outer structure, the
top end of said inner structure being secured to the hull; [0022]
said bottom wall of the watertight outer structure having a
plurality of said pipes passing therethrough in leaktight manner,
which pipes pass through and are supported by said inner structure;
[0023] said watertight outer structure not being supported by said
hull nor being fastened to said hull, and having dimensions that
enable it to float naturally in the water in the cavity in said
floating support; [0024] said inner and outer tubular structures
co-operating with at least one bottom rolling or friction bearing,
preferably a rolling bearing, allowing said inner structure to
turn, said outer structure being prevented from turning when said
floating support is caused to turn about said vertical axis ZZ' of
the cavity and of said watertight tubular outer structure; and
[0025] said bottom rolling or friction bearing being situated below
the surface of the water but inside said watertight outer
structure.
[0026] This configuration for the mooring system and the rolling or
friction bearing in accordance with the present invention is
particularly advantageous compared with the prior art, since said
rolling bearing is in the dry and is accessible from inside the
inner and/or outer structures without it being necessary to work
under water, with this applying both to the personnel involved and
to the equipment. By way of example, rolling means may thus be
maintained easily, in particular they may be greased regularly,
thereby greatly reducing friction and making it easier for the FPSO
to turn about its turret. In addition, rolling elements may easily
be changed under all conditions, in particular even during a storm
and not only in calm weather.
[0027] In a preferred embodiment, said floating support includes at
least one "support" bottom rolling bearing interposed between the
bottom wall of said watertight tubular outer structure and the
bottom end of said inner structure.
[0028] It can be understood that said rolling bearing is situated
above said bottom of the turret and below said inner structure.
[0029] It can be understood that when said inner structure is
constituted by a tubular structure of circular section at its
bottom end, said bearing is interposed between said bottom of the
outer structure and the circular edge face at the circular section
bottom end of said inner structure.
[0030] Also preferably, said floating support includes: [0031] at
least one bottom "guide" lateral rolling bearing interposed between
the inner side surface of said outer tubular structure and the
outer side surface of said inner structure, said bottom lateral
guide bearing being situated below the level of the water surface
and closer to said bottom wall of said tubular outer structure than
to the top end of said tubular outer structure, preferably in the
vicinity of said bottom wall; and [0032] at least one top "guide"
lateral rolling bearing interposed between the inner side surface
of the outer tubular structure and the outer surface of said inner
structure, said bearing being situated closer to the top end of
said tubular outer structure than to the bottom of said tubular
outer structure, preferably in the vicinity of the top end of the
inner structure.
[0033] In a particular embodiment, said rolling bearing(s) is/are
constituted by rollers or by wheels.
[0034] It can be understood that said rollers or wheels are
disposed with their axes of rotation in a substantially vertical
position interposed between said inner and outer structures for
said top and bottom lateral guide bearings; and for said bottom
support bearing, said rollers or wheels are disposed with their
axes of rotation in substantially horizontal positions.
[0035] More particularly, said rollers or wheels are disposed
circularly around said inner structure, preferably being regularly
spaced apart circularly in the annular space between said inner and
outer structures, and preferably being regularly spaced apart on
said bottom of the outer structure, being disposed in a circle.
[0036] Advantageously, said outer and inner tubular structures
include abutment means and retaining means preventing said outer
structure from sinking in the event of sea water accidentally
flooding the inside of the outer tubular structure due to loss of
watertightness, said abutment means and said retaining means
enabling the outer structure to be retained by said inner
structure.
[0037] It can be understood that since said inner structure is held
securely to the hull by bearing thereon at its top end, said
retaining means prevent said outer structure from dropping below
said floating support.
[0038] In a particular embodiment, said inner structure includes at
its top end a top peripheral plate via which said inner structure
is secured to the hull of said floating support, preferably said
top face bearing via a step in the top end of said cavity, more
preferably in such a manner that said top plate does not project
above the level of the deck of the floating support.
[0039] Still more particularly, said top plate bears against a step
in the top end of said cavity, preferably in such a manner that
said top plate does not project above the level of the deck of the
floating support.
[0040] Advantageously, said inner structure contains a carrier
structure, preferably in the form of a central pillar, preferably
of circular section, that rests on the bottom wall of said tubular
outer structure and that extends up to the level of the deck of the
floating support, said carrier structure holding said second pipes
passing through the inner structure in a supported position, and
preferably also supporting said rotary joint coupling resting on
top of said carrier structure level with the deck of the floating
support.
[0041] In a particular and advantageous embodiment of the
invention, said buoy includes a top tubular wall, preferably of
circular section, defining a "valve" chamber when the top edge of
the tubular top wall of the buoy is pressed against the bottom wall
of the turret, said valve chamber containing the top ends of said
first pipes passing through the bottom wall of said valve chamber,
the top ends of said first pipes being fitted with vales and/or
with male or female automatic connector portions supported by said
bottom wall of the valve chamber, and said buoy including in its
bottom portion an annular box constituting a float under the bottom
wall of the valve chamber.
[0042] Other aspects of the problem and other characteristics and
advantages of the present invention appear more clearly in the
light of the following detailed description made in illustrative
and non-limiting manner with reference to the drawings, in
which:
[0043] FIG. 1 is a side view in section of an FPSO anchored on a
turret within pack ice;
[0044] FIG. 2 is a section view on plane AA of FIG. 1 showing the
FPSO and the turret of the invention in section, without showing
said mooring buoy (1) nor the rotary joint coupling (3) at the deck
of the hull;
[0045] FIG. 2A is a section view of the turret subjected to
buoyancy thrust;
[0046] FIG. 2B is a section view on BB of FIG. 2A through a bottom
rolling bearing;
[0047] FIG. 2C is a section view of the FPSO showing its cavity
that receives the turret;
[0048] FIG. 2D is a diagrammatic section view of a prior art
turret;
[0049] FIG. 3A is a section view on plane AA of FIG. 1 showing the
FPSO and the turret of the invention in section with the mooring
system including the turret of the invention, the mooring buoy
supporting the anchor lines and the flexible pipes, said buoy being
connected to the base of the turret with a rotary joint coupling
(3) level with the deck of the floating support; and
[0050] FIG. 3B shows the mooring buoy being cast off to allow the
FPSO to take shelter.
[0051] FIG. 1 is a side view in section showing a ship or floating
support of the FPSO type 10 anchored on a turret of a releasable
mooring system 1, 2, 3 anchored by anchor lines 13 and connected to
undersea well heads (not shown) via flexible pipes 14 in a dipping
catenary configuration 14a going down to a subsurface float 15
supporting said pipe, said float being held by a cable 15a
connected to a mooring block or "deadman" 15b at the bottom of the
sea, after which said flexible pipe 14a extends in a catenary
configuration 14b down to the bottom of the sea 40 and then to said
well heads. The FPSO is in cold water in which icebergs or pack ice
31 of large area and considerable thickness can be present floating
on the surface of the sea 32. In certain extreme conditions, such
as storms or when the pack ice is so thick that the ice
breaker-shaped bow of the ship cannot break it as it advances, it
is necessary to disconnect the FPSO to allow it to take shelter
while waiting for the situation to return to normal. For this
purpose, the bottom portion 1 of the mooring system, commonly
referred to as a "spider buoy" is constituted by an annular mooring
buoy 1 that can be disconnected in a manner known to the person
skilled in the art, generally from the bottom of the FASO, thereby
enabling said FPSO to be released so that it can take shelter. More
particularly, the mooring buoy 1 and the first underwater pipes 14
are connected to said bottom wall 2c of the turret via the bottom
face of the bottom wall 2c by means of automatic connectors 7. The
internal buoyancy of the annular mooring buoy 1 is adjusted in such
a manner that said buoy stabilizes at a height H above the bottom
of the sea, e.g. corresponding to a distance of 100 m from the
surface of the sea 32, thereby putting all of the anchor lines and
pipes in a sheltered position, as also shown in FIG. 1.
[0052] In FIGS. 3A and 3B, there can be seen the entire
disconnectable mooring system 1, 2, 3 of the present invention
including an annular mooring buoy 1: [0053] said mooring buoy is
fastened under the hull of the floating support, at the bottom face
of the bottom wall 2c of the turret 2, said turret extending over
the full height of a cavity 4 passing through the entire height of
the hull of the floating support; [0054] said turret 2 is rotatably
mounted relative to said hull by means of three rolling bearings
5.sub.1, 5.sub.2, 5.sub.3, as described below, enabling said
floating support to turn about a vertical axis ZZ' of said turret
and of said cavity without causing said mooring buoy to turn; and
[0055] said mooring buoy enables the underwater top ends of the
first bottom-to-surface connection pipes 14 to be connected to the
bottom ends of second pipes 14c rising within the cavity 4 up to a
rotary joint coupling 3 located level with the deck 10.sub.1 of the
hull at the top end of a central pillar of a carrier structure 6
supporting the pipe sections 14 that provide the connection between
the bottom wall 2c of the turret and the rotary joint coupling
3.
[0056] The second pipes 14c pass through the bottom wall 2c of the
turret from a female portion 7b of the automatic connector under
the bottom wall 2c at the bottom ends of the second pipes. These
automatic connector female portions 7b co-operate with automatic
connector male portions 7a at the top ends of the first pipes 14
carried by and moored to said buoy 1, thereby enabling the first
and second pipes to be connected together.
[0057] The top portion of the mooring buoy 1 is constituted by a
top tubular wall 1a, preferably of circular section, defining a
chamber 30 containing the top ends of the first pipes 14 passing
through the bottom 30a of the chamber 30, said top ends of the
first pipes 14 and the bottom ends of the second pipes 14c being
fitted with respective valves 8a and 8b and with the male portions
7a and the female portions 7b respectively of the automatic
connectors 7. An annular gasket is applied against the top edge 1b
constituting the edge face of the top tubular wall 1a of the
mooring buoy 1.
[0058] The valves 8a and the male portions 7a of the automatic
connectors 7 at the top ends of the first pipes 14 are supported by
the bottom 30a of the valve chamber 30.
[0059] The valves 8b and the female portions 7b of the automatic
connectors 7 at the bottom ends of the second pipes 14c are
supported by the bottom wall 2c of the turret.
[0060] The mooring buoy 1 has a bottom portion 1c forming an
annular box constituting a float under the bottom wall 30a of the
valve chamber 30.
[0061] In known manner, the rotary joint coupling 3 is mounted to
be free to rotate so as to allow said floating support to turn,
without turning said coupling and the pipes that are connected
thereto at the floating support.
[0062] FIG. 2 is a side view in section shown the FPSO in section
on plane 2A of FIG. 1. The turret 2 is installed in a preferably
circular cavity 4 passing vertically through the entire height of
the FPSO 10, from its deck 10.sub.1 down to the bottom of its hull.
The top portion of the cavity 4 presents a step 10a matching the
top portion 2a.sub.1 of the turret. Sea water is present inside
said cavity 4 of the FPSO and the turret naturally floats in said
cavity since buoyancy thrust acts on an external structure 2b of
the turret 2.
[0063] To clarify the figures, the guide and support bearings are
shown as being constituted by rollers that are in contact on one
side with the outer structure 2b and on the other with the inner
structure 2a, however it is advantageous to use devices having
wheels turning about axles, said wheels coming directly into
contact with one of the structures, e.g. the outer structure 2b,
and the axles of the said wheels being supported by the other
structure, i.e. the inner structure 2a.
[0064] FIG. 2A is a side view in section showing the operation of
the turret subjected to buoyancy thrust, and for greater clarity of
explanation, the hull of the FPSO is omitted. The turret 2 is
constituted by: [0065] an internal structure 2a secured to the
FPSO, having a peripheral plate 2a.sub.1 at its top end that
co-operates with the FPSO by bearing thereagainst and by being
secured thereto, in particular by welding and/or by bolting,
preferably at the level of the deck of said FPSO, and more
particularly via a step 10a of said FPSO. The internal structure 2a
is a tubular structure, preferably a substantially circular
structure, and it extends over substantially the entire height of
the turret; and [0066] a watertight tubular outer structure 2b that
is preferably substantially circular, coaxial about the tubular
inner structure 2a, and having a bottom 2c that is assembled in
watertight manner to said outer structure 2b, said bottom having a
plurality of pipes 14 passing therethrough in watertight
manner.
[0067] For greater clarity, the figures show only one pipe 14
passing through the bottom 2c.
[0068] The internal structure may be a lattice-work structure
constituted by an assembly of girders. The mooring system in the
turret has three rolling bearings, namely: [0069] a top bearing
5.sub.3 for lateral guidance; and [0070] a bottom bearing 5.sub.2
for lateral guidance; and [0071] a bottom bearing 5.sub.1 for
support.
[0072] Said bearings 5.sub.1, 5.sub.2, and 5.sub.3 are friction
bearings or rolling bearings, and they are preferably rolling
bearings. More particularly, they may comprise rollers interposed
between the inner structure 2a and the outer structure 2b, and they
may be optionally be supported by the inside face of the outer
structure 2b or by the outside face of the inner structure 2a.
[0073] It can be understood that at least at said bearings, said
inner structure and said outer structure present sections that are
circular. Said top and bottom bearings 5.sub.2, 5.sub.3 that
provide lateral guidance are placed in the annular space between
the outer and inner side surfaces of said inner and outer
structures respectively, and they are preferably regularly spaced
apart around the periphery in a circular configuration. The rollers
of the bottom and top lateral guide bearings 5.sub.2 and 5.sub.3
are more particularly disposed with vertical axes. For the bottom
support bearing 5.sub.1, said rollers are disposed with horizontal
axes. They are advantageously supported by the edge face of the
inner structure at its bottom end.
[0074] Since the outer structure 2b is watertight, buoyancy thrust
acts on the entire volume of displaced water, so said outer
structure tends to rise towards the surface, however it then comes
into contact via the bottom 2c with the bottom end of the tubular
inner structure 2a, via a support bearing 5.sub.1.
[0075] By way of example, in order to install a large number of
pipes, for gas, for crude oil, for hydraulic umbilical connections,
and for electrical cables, e.g. 36 or 48 pipes 14, all having their
corresponding safety and control elements, as shown in FIG. 5, the
outside diameter of said outer structure 2b may exceed 25 m, and
more particularly may be about 10 m to 20 m, and its wetted height
is generally greater than 20 m, and may be as much as 25 m or even
more when the hull of the floating support extends over a height of
50 m, as is sometimes the case. For an outer structure having a
height of 20 m to 25 m and a diameter of 10 m to 20 m, this
represents a vertical buoyancy thrust F of the order of 8000 metric
tonnes (t) to 12,000 t. This considerable, upwardly-directed
vertical force is transmitted to the inner structure 2a via the
bottom support bearing 5.sub.1, and then to the hull of the FPSO
via the peripheral plate 2a.sub.1 secured to said FPSO in the step
1a.
[0076] The inner and outer tubular structures have a common
substantially vertical axis of rotation ZZ defined by the lateral
guide bearings 5.sub.2, 5.sub.3, thereby enabling the FPSO to turn
freely about said axis ZZ even though the annular mooring buoy 1
secured to the outer structure 2b presents an orientation relative
to said axis ZZ that is substantially stationary relative to the
sea bed.
[0077] The top and bottom lateral guide bearings 5.sub.3 and
5.sub.2 then enable the FPSO to turn about the substantially
vertical axis ZZ with minimal friction and wear when the FPSO is
subjected to horizontal forces due to pack ice, swell, wind, or
even current.
[0078] Compared to the prior art, this disposition is advantageous
since the means for guiding the turret in the bottom portion of the
FPSO are not in contact with sea water, but are in the dry and are
therefore accessible from inside the structure. The running tracks
can thus be maintained and greased regularly, thereby greatly
reducing friction and facilitating turning of the FPSO on its
turret. In addition, individual bearing elements can easily be
changed at any time. Naturally, these maintenance operations are
preferably carried out in calm weather, after taking care to block
rotation of the turret temporarily by means that are not shown.
[0079] Buoyancy thrust thus naturally holds the inner and outer
structures 2a and 2b of the turret 2 in position, however a safety
device is advantageously added in order to avoid the outer
structure 2b dropping downwards, e.g. in the event of the turret
becoming filled with water as a result of a valve breaking or of a
leak through the watertight structure of said outer structure 2b.
For this purpose, a series of abutments and catches
2d.sub.1-2d.sub.2 are arranged in circular manner between said
outer structure and said inner structure to prevent said outer
structure from dropping downwards if it becomes flooded. For
example, an abutment 2d.sub.1 is fastened to the outer portion of
the structure 2b, while a catch 2d.sub.2 is movable in horizontal
translation and is located within the inner structure 2a below the
corresponding abutment 2d.sub.1. Said catch 2d.sub.2 is shown in a
retracted position in the left-hand portion of FIG. 2A and in a
deployed position for retaining the abutment 2d.sub.1 in the
right-hand portion of FIG. 2A in the event of the outer structure
2b having a tendency to sink. A similar catch is advantageously
used to prevent the turret from turning during maintenance
operations.
[0080] When the ship is highly stressed, whether by pack ice or by
swell, wind, or current, its anchor system connected to the annular
mooring buoy 1 holds it in position. Given the large dimensions of
the FPSO, the reaction forces on the anchoring give rise to
considerable variations in horizontal tension H, which may be as
great as 5000 t to 7500 t in the event of pack ice advancing
perpendicularly to the side of the FPSO, and as great at 1500 t to
3000 t under extreme conditions of swell, wind, and current. These
horizontal forces are transmitted to the annular mooring buoy.
[0081] FIGS. 3A and 3B show a carrier structure in the form of a
central pillar of circular section 6 resting on the bottom 2c of
the outer structure 2b of the turret and serving both to support
the pipes 14 passing through the cavity 4 in order to reach the
rotary joint coupling 3, and also to support the rotary joint
coupling 3 itself at its top, substantially level with the deck of
the floating support 10.
[0082] The invention is described above with a support bearing
5.sub.1 situated between the bottom of the inner structure 2a and
the bottom of the watertight outer structure 2b, however, in a
variant of the invention, said support bearing is situated at the
top of the watertight outer structure 2b, between the outer
structure and the inner structure, level with the underface of the
peripheral plate 2a.sub.1.
* * * * *